240V extension cords exist, but most people shouldn't use them.

Yes, but be careful. A standard 120V extension cord will fry itself on 240V, and you’ll get a melted mess or a fire.

For a window air conditioner or welder, you need a cord rated for 240V and the correct amperage—usually 15A or 20A for ACs, 30A or more for welders. That means thick wire (e.g., 10 AWG for 30A) and the right plug (NEMA 6-15 or 6-20). Most hardware stores sell them, but they’re not cheap and length matters: longer = more voltage drop = poor performance.

Honestly, try to avoid them. Window ACs should plug into a dedicated 240V outlet if possible. Welders often specify a maximum cord length and gauge in the manual—follow that strictly.

If you’re asking, you probably shouldn’t.